Biology of the Brain - Key Points
The Brain - General Features
- The brain is the most complex structure in the known Universe!
- It possesses many highly specialized component parts each associated with specific
tasks, for example memory and vision.
- The functioning of the human brain not only allows us to sense our environment and
coordinate movements but also gives rise to attributes such as consciousness.
- The latter is difficult to define but includes such attributes as a sense of past and
future, an inner voice and self-awareness. Intelligence appears to be the outward sign of
a conscious being.
- It is the result of millions of years of evolution - the distant origins of the human
brain can be seen in simple reptiles and mammals.
The Human Cortex
- The most striking feature of the human brain is seen in the cortex. This is the folded,
hemispherical structure which constitutes the bulk of the visible brain.
- It is not present in reptiles.
- The cortex is relatively recent. It is perhaps one hundred thousand years old and is the
part of the brain most closely associated with our ability to form complex representations
of the external world, to reason logically and to use language.
- It is much more dominant in humans than in any other species.
- Regions of the cortex control vision, our auditory senses, voluntary movement and touch
sensations. It is also crucial for long term memory.
Neurons and Networks
- The central nervous system is composed of something like one hundred billion nerve cells
- Each nerve cell or neuron possesses a single axon along which it can pass electrical
signals to other neurons. Incoming signals are carried by a neuron's dendrites which form
a tree-like structure around the neuron.
- Neurons are about one micron (1 millionth meter) in diameter. The dendrites are perhaps
ten times this in length while the axon varies from a millimeter up to one meter in
- The signal from one neuron reaches another at the junction of axon and dendrite -- the
- The typical voltages associated to these signals are small (tens of millivolts) and
travel at about two hundred miles an hour (100 meters per second)
- Typically neurons can only fire once every millisecond (one thousandth of a second)
- Different patterns of electrical firing activity are associated with different brain
Learning and Connections
- The brain is both robust (able to function in the event of severed connections and/or
dead neurons) and plastic - able to adapt to new memories and functions.
- This is due to ability of the brain to form new connections between neurons. These
connections take place at synapses and are mediated by the release of neurotransmitter
- These neurotransmitters alter the effective strength of the signal which can pass
- During our early years and during any kind of learning process these connections form
and change their strengths.
- The power of the brain as a computational device derives from the complex network of
neural pathways and the simultaneous processing capability of all the neurons.
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